1. Field of the Invention
The present invention relates to a hydrogen production process, more particularly to a hydrogen production process initiated at a lower ambient reactor temperature and producing hydrogen at a lower reaction temperature.
2. Description of the Related Art
Fuel cells capable of converting chemical energy of the fuel into electricity and also satisfying the requirement of environmental protection are now being continuously developed. Proton exchange membrane fuel cells (PEMFCs) take advantage of lower operation temperature and are of great potential among those developing fuel cells. However, PEMFCs have disadvantages in storage and transportation of hydrogen. Hydrocarbon molecules are used as the external primary fuel in PEMFCs and converted into hydrogen rich gas (HRG) on site. HRG is gas mixture with high hydrogen content and one of environmentally friendly fuels applied in fuel cells.
Production of HRG from reforming of methanol has been widely studied because of being highly chemically active, abundant, and cheap. Many methanol reforming processes have been developed and published in literatures, including (1) “methanol decomposition” (MD) process, (2) “steam reforming of methanol” (SRM) process and (3) “partial oxidation of methanol” (POM) process, which may be expressed by the following chemical formulas.CH3OH→2H2+CO ΔH=90.1 kJmol−1   (1)CH3OH+H2O→3H2+CO2 ΔH=49 kJmol−1   (2)CH3OH+½O2→2H2+CO2 ΔH=−192 kJ mol−1   (3)
CO is not only one main product generated in the MD process but also a contaminant for the platinum electrodes of the fuel cells. SRM process has high hydrogen yield (number of hydrogen molecule produced per each methanol molecule consumed) of RH2=3.0. However, SRM process is an endothermic reaction which is not theoretically favored at low temperatures according to Le Chatelier's Principle and tends to be efficient at high temperature (>250° C.).
POM process is another known process for hydrogen production process in literatures. Different from SRM process, the POM process is an exothermic reaction. Once reaching the initiation temperature, the POM process will persist autonomously without external heat energy. Therefore, the POM process consumes less energy and requires a smaller reactor and a lower cost.
There have been many researches about catalysts for the POM process. For example, catalysts containing Cu, Zn, Ce, Zr, and Pd are disclosed in a US patent of publication No. 20070269367 by Wolf et al. The aforementioned catalysts need a higher temperature (>200° C.) to attain a better catalytic activity for the POM reaction. Further, a carbon monoxide (CO) selection ratio for the aforementioned reaction is as high as about 10%, and high CO content in the HRG will poison the platinum catalyst in PEMFCs, abruptly impair the catalytic function and thus lower the performance of PEMFCs. The performances of POM catalysts adopted in the following papers are listed in Table.1, including Pd/ZnO (M. L. Cubeiro, J. L. G. Fierro, Appl. Catal. A 168 (1998) 307), Cu/ZnO (T. Bunluesin, R. J. Gorte, G. W. Graham, Appl. Catal. B 14 (1997) 105), Cu/ZnO— Al2O3 (S. Velu, K. Suzuki, T. Osaki, Catal. Lett. 62 (1999) 159, US patent of publication No. 20050002858), Cu/Cr-ZnO (Z. F. Wang, J. Y. Xi, W. P. Wang, G X. Lu, J. Mol. Catal. A: Chemical 191 (2003) 123), and CuPd/ZrO2—ZnO (S. Schuyten, E. E. Wolf., Catal. Lett. 106 (2006) 7, US patent of publication No. 20070269367).
TABLE 1Effects of Catalysts on the POM ReactionReactionTemperatureCMeOH SH2SCOCatalyst(° C.)(%)(%)(%)Pd/ZnO250709619Cu/ZnO320789810Cu/ZnO—Al2O3245839812Cu/Cr—ZnO200866812CuPd/ZrO2—ZnO200898811
According to Table.1, these catalysts share a common drawback in catalytic effect on the POM reaction that they could only have good catalytic activity in conditions of higher temperature (>220° C.).
Nojima et al (U.S. Pat. No. 6,576,217) and Wolf (US Patent Application 20070269367) both disclose that cerium oxide is a useful component for catalysts for the partial oxidation of methanol. However, none of Nojima and Wolf has disclosed a POM process at a lower initiation temperature (<100° C.) and reaction temperature (<200° C.).
As all the Cu and Pd containing catalysts in the cited papers need a reaction temperature over 200° C., the POM process needs a step of pre-heating and start-up, which is likely a bottleneck for initiation time. PEMFCs and reduces the practicability of PEMFCs. Once the initiation temperature and reaction temperature of the POM process are lowered, the start-up time of PEMFC, electric vehicles and electronic products would be shortened. Furthermore, the power consumption and cost thereof would also be reduced.